LeapSecondFile Class

The LeapSecond.dat file is an ASCII text file which contains the dates of all historical and announced leap seconds that would affect the conversion between the UTC time scale and other time scales.

The latest file containing all known leap seconds can be found at https://ftp.agi.com/pub/STKData/Astro/LeapSecond.dat. The information in the file is obtained from the U.S Naval Observatory leap second information file.

The format of the LeapSecond.dat file consists of an initial line with an integer value indicating the number of leap second entries that the file contains, followed by a leap second entry on each subsequent line of the file.

A leap second entry consists of the following space-delimited information:

• The Gregorian calendar 4-digit year, abbreviated month name, and day of the date immediately following the leap second.
• The corresponding Julian date.
• The difference between TAI and UTC time scales (the accumulated number of leap seconds) as of the corresponding date.
• The modified Julian date of the epoch at which the following rate is established. Obsolete as of 1 Jan 1972. Since then, the value of this epoch has been defined as 41317.0. This value is not read from the file, and is not used.
• The rate at which the UTC time scale is slowing with respect to the TAI time scale. Obsolete as of 1 Jan 1972. Since then, the value of this rate has been defined as 0.0. This value is not read from the file, and is not used.

The following is an example of a leap second file in this format:

28
 1972 JAN  1   2441317.5     10.0        41317.  0.0
 1972 JUL  1   2441499.5     11.0        41317.  0.0
 1973 JAN  1   2441683.5     12.0        41317.  0.0
 1974 JAN  1   2442048.5     13.0        41317.  0.0
 1975 JAN  1   2442413.5     14.0        41317.  0.0
 1976 JAN  1   2442778.5     15.0        41317.  0.0
 1977 JAN  1   2443144.5     16.0        41317.  0.0
 1978 JAN  1   2443509.5     17.0        41317.  0.0
 1979 JAN  1   2443874.5     18.0        41317.  0.0
 1980 JAN  1   2444239.5     19.0        41317.  0.0
 1981 JUL  1   2444786.5     20.0        41317.  0.0
 1982 JUL  1   2445151.5     21.0        41317.  0.0
 1983 JUL  1   2445516.5     22.0        41317.  0.0
 1985 JUL  1   2446247.5     23.0        41317.  0.0
 1988 JAN  1   2447161.5     24.0        41317.  0.0
 1990 JAN  1   2447892.5     25.0        41317.  0.0
 1991 JAN  1   2448257.5     26.0        41317.  0.0
 1992 JUL  1   2448804.5     27.0        41317.  0.0
 1993 JUL  1   2449169.5     28.0        41317.  0.0
 1994 JUL  1   2449534.5     29.0        41317.  0.0
 1996 JAN  1   2450083.5     30.0        41317.  0.0
 1997 JUL  1   2450630.5     31.0        41317.  0.0
 1999 JAN  1   2451179.5     32.0        41317.  0.0
 2006 JAN  1   2453736.5     33.0        41317.  0.0
 2009 JAN  1   2454832.5     34.0        41317.  0.0
 2012 JUL  1   2456109.5     35.0        41317.  0.0
 2015 JUL  1   2457204.5     36.0        41317.  0.0
 2017 JAN  1   2457754.5     37.0        41317.  0.0

EarthOrientationParametersFile contains EarthOrientationParameters which describe the motion of the Earth's spin axis (pole wander) and the irregular rotation rate of the Earth. These parameters are used in the computation of the transformation between the Earth centered fixed reference frame and Earth centered inertial frames. At the time of a leap second, the time history of the Earth's irregular rotation rate experiences a discontinuity of 1 second. It is therefore important that the Earth orientation parameters and leap second information be updated together to properly establish the existence of the new leap second.

This example shows how to load leap second data from a file and use it in the current calculation context:

LeapSecondsFacet leapSeconds = LeapSecondFile.ReadLeapSeconds(filename);
leapSeconds.UseInCurrentContext();

This example shows how to download leap second data over the internet from an AGI server, and use it in the current calculation context:

LeapSecondsFacet leapSeconds = LeapSecondFile.DownloadLeapSeconds();
leapSeconds.UseInCurrentContext();

Reference